How much deeper is a wider tyre?

[jay clock]

I am going off touring in the USA. One of the people I am going with is taking a Gunnar Roadie bike, and is trying to work out what bigger tyres she can fit. I live miles away so cannot easily look

Currently has 23mm tyres. Is there a way to know how much deeper 25mm or 28mm will be? I assume someone will know?

Jay

 

[smutchin]

Tyres should in theory have a round profile so height and width should be the same (or very nearly), but in reality it will depend on other factors like rim width and tread depth. Also bear in mind that two 25c tyres from different brands may actually be different sizes in practice.

If she can measure the height and width of the existing tyres (using vernier calipers), that might give an idea.

 

[Gravity Aided]

You might also check the tire manufacturers' website, they may have an idea, as well as rim width recommendations for different sized tires.

 

[smutchin]

Also check how much clearance the frame has - prodding an allen key into the gap (between fork crown/front tyre, brake bridge/rear tyre) is an easy way to do this.

For example, if you can fit a 5mm allen key into the gap, it's probably safe to go from 23 to 25, but probably not safe to go to a 28.

 

[mjr]

Tyres should in theory have a round profile so height and width should be the same, [...]

Some manufacturers do give a height after the width, such as some Schwalbe tyres being labelled 28/32-630.

 

[smutchin]

Some manufacturers do give a height after the width, such as some Schwalbe tyres being labelled 28/32-630.

Marathon Plus? I can well imagine that's the case with tyres that have a deep layer of puncture protection under the tread.

 

[mjr]

Marathon Plus? I can well imagine that's the case with tyres that have a deep layer of puncture protection under the tread.

The example given is HS-159. I've not check Marathon Plus - or actually checked my HS-159 to see if they measure up as marked. But the theory is there...

 

[smutchin]

The example given is HS-159. I've not check Marathon Plus - or actually checked my HS-159 to see if they measure up as marked. But the theory is there...

I'm intrigued by this as it's not something I've encountered before... So the HS159 are deliberately constructed to be taller than they are wide? Bonkers.

I checked Schwalbe's website and the spec for M+ (all varieties) doesn't give separate dimensions for height and width, only a single [width] dimension.

 

[smutchin]

I believe the width is the tyre’s internal dimension. Therefore, if you had deep tread or puncture protection on the outside that would also need to be taken to account.

That's what I thought, hence my wondering if this would apply to the M+ but it doesn't so I'm confused.

The HS159 doesn't appear to have the same level of puncture protection as M+, nor an especially deep tread.

 

[mjr]

That's what I thought, hence my wondering if this would apply to the M+ but it doesn't so I'm confused.

The HS159 doesn't appear to have the same level of puncture protection as M+, nor an especially deep tread.

Well, it stopped snowing at lunchtime so I went for a quick measure and they are definitely 28mm wide (calipers) and 32mm deep seems plausible (holding a depth gauge alongside) but it's difficult to be sure while they're inflated, uncut and on the rim. I'm fairly sure they're deeper than 28mm and I don't remember the rim width - maybe 16mm?

Edit: but if it's not stated, assume the same height as width and you're probably correct. These are unusual nowadays

 

[Bodhbh]

I measured how fat some 60mm Big Apples actually were a while back. First I took a wheel out the rear triangle and measured the width of the chain and seat stays where the tyre sits, then I measured the clearance left when the tyre was in there (this was just with a tape measure). Subtracting clearance from the width, it was pretty much 60mm spot on. I repeated this with a couple of other tyres (Surly Knard and Dirt Wizard) and got similar results.

I know the manufacturers measurements are nominal, and also other factors like pressure and rim width will have a slight bearing, but unless you're really trying to push it, I would take them as given and allow a few mm as appropriate for error (less for road tyres than MTB I'm guessing).

/doh - just noticed it's depth. I would think it scales similarly to the width...incidentally, Surly gives tyres 'geometries' on their website, including depth, but it's almost only their fat tyres. The 42mm Knard looks like it's 47.5mm deep on 24mm rims, with 41mm or 42mm width, depending whether you measure casing or knobbles.

 

[Ajax Bay]

Rollingresistance.com
gives both height and width (and much more), testing tyres described as 622-25, mounted on a 622-17 rim as standard and at 100psi. I have found this is the best site and hopefully the OP's riding partner should find possible tyre choices there which will at least indicate whether they come up wide/deep or narrower than ETRTO description.
This will augment the useful and accurate advice (posts #2 and #4) from @smutchin above.

 

[GuyBoden]

Also check how much clearance the frame has - prodding an allen key into the gap (between fork crown/front tyre, brake bridge/rear tyre) is an easy way to do this.

For example, if you can fit a 5mm allen key into the gap, it's probably safe to go from 23 to 25, but probably not safe to go to a 28.

Using wider tyres with little clearance on resurfaced roads with loose chippings can be very dangerous..................

http://road.cc/content/news/127430-petition-against-surface-dressing-gets-10000-signatures

 

[Ajax Bay]

Do they do surface dressing in America? That's where the OP is doing his long ride.
A bit off topic, imo.

 

[boydj]

Ask her to send a couple of photos of the front and rear clearances as they are now, to give you an idea of the scope you have for bigger tyres.